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Synopsis: Information regarding Lassa fever, an acute viral illness that is endemic in parts of west Africa.

Definition:

Lassa fever or Lassa hemorrhagic fever (LHF) is an acute viral hemorrhagic fever caused by the Lassa virus and first described in 1969 in the town of Lassa, in Borno State, Nigeria. Lassa fever is a member of the Arenaviridae virus family. Similar to ebola, clinical cases of the disease had been known for over a decade but had not been connected with a viral pathogen.

Lassa fever is an acute viral illness that occurs in west Africa. The illness was discovered in the year 1969 when two missionary nurses died from it in Nigeria. The virus is named after the town in Nigeria where the illness first occurred. The virus is a member of the virus family, ‘Arenaviridae,’ and is a single- stranded RNA virus; it is, ‘zoonotic,’ or animal-borne. Lassa fever is endemic in parts of west Africa, to

include the following areas:

Liberia

Guinea

Nigeria

Sierra Leone

Neighboring countries are also at risk due to the animal vector for Lassa virus. The animal is the,

‘Lassa Fever Blog,’ which is distributed throughout the region as a whole. In the year 2009, the first case from Mali was reported in a traveler who was living in southern Mali.

Ghana reported its first cases in the year 2011. Isolated cases have been reported in Cote d’Ivoire and Burkina Faso. There is also seismologic evidence of Lassa virus infection in Benin and Tongo.

The number of people who experience Lassa fever each year in west Africa is estimated to be between 100,000 and 300,000, with around 5,000 people dying from the virus. The estimates are crude because surveillance for cases of the disease is not performed uniformly. In some areas of Liberia and Sierra Leone, approximately 10-16% of those admitted to hospitals each year have Lassa fever, which indicates the serious impact of the virus on the population of these areas.

Signs and Symptoms of Lassa Fever.

The signs and symptoms of Lassa fever commonly happen 1-3 weeks after a person has come into contact with the virus. For most of those with a Lassa fever virus infection; around 80%, symptoms are mild and under-diagnosed. Mild symptoms include:

Weakness

Headaches

Slight fever

General malaise

Around 20% of infected people; however, the disease might progress to more serious symptoms that include hemorrhaging of the person’s eyes, gums, or nose – repeated vomiting, respiratory distress, pain in the back, chest and abdomen, facial swelling and shock. Neurological issues have also been described in relation to Lassa fever, to include tremors, hearing loss and encephalitis. An infected person may die within two weeks of their initial symptoms because of multi-organ failure. The most common complication of Lassa fever is deafness. Different degrees of deafness happen in around one-third of those who become infected. In many cases, the hearing loss is permanent. The severity of the disease does not affect this particular complication; deafness might develop in mild as well as severe cases.

Between 15-20% of people who are hospitalized for Lassa fever die from the illness. Only 1% of all Lassa virus infections; however, result in the person’s death. The death rates for women in the third trimester of pregnancy are exceptionally high. Spontaneous abortion is a very serious complication of the infection; an estimated 95% mortality rate in fetuses of infected mothers is an alarm sounding off.

Due to the fact that the symptoms of Lassa fever are so nonspecific and varied, clinical diagnosis is often times difficult. Lassa fever is also associated with occasional epidemics. During these epidemics, the fatality rate may reach as high as 50% in people who become hospitalized.

Diagnosing Lassa Fever

Lassa fever is most often diagnosed through the use of, ‘enzyme-linked immunosorbent serologic assays (ELISA), which detect IgM and IgG antibodies as well as Lassa antigen. Reverse transcription- polymerase chain reaction (RT-PCR) may be used in diagnosing people who are in the early stage of the disease. The Lassa virus itself may be cultured in 7-10 days, yet the procedure should only be performed in a high containment laboratory with good laboratory practices. Immunohistochemistry, performed on formalin-fixed tissue specimens, might be used to make a post-mortem diagnosis.

Treating Lassa Fever

‘Ribavirin,’ is an antiviral drug that has been used with success in people affected by Lassa fever. It has been shown to be most effective when it is administered early in the course of the illness. People should also receive supportive care that consists of maintenance of:

Oxygenation

Blood pressure

Treatment of complicating infections

Appropriate fluid and electrolyte balance

Preventing Lassa Fever

Primary transmission of the Lassa virus from its host to people may be prevented by avoiding contact with Mastomys rats – particularly in the geographic areas where outbreaks happen. Putting food away in rat-proof containers and keeping your home clean help with discouraging rats from entering your home.

Using these rats as a source of food is definitely not recommended. Trapping around and in homes may help to reduce rat populations. Yet the wide distribution of Mastomys rats in Africa makes complete control of these rats impractical. While providing care for people with Lassa fever, further transmission of the disease through person-to- person contact or other routes may be avoided by taking preventative precautions against contact with secretions from infected persons called, ‘VHG isolation precautions,’ or barrier nursing methods. The precautions include wearing protective clothing such as masks, gowns, gloves and goggles; using infection control measures such as the sterilization of equipment. It is vital to isolate infected people from contact with unprotected persons until the disease has run its course.

In addition, educating people who live in high-risk areas about ways to lower the rat populations in their homes will help to control and prevent Lassa fever. Other challenges include the development of quicker diagnostic tests and increasing the availability of the one drug known for treatment of Lassa fever – ribavirin. Research is currently being performed in regards to the development of a vaccine for the illness.

Facts: Lassa Fever

While most humans are infected either from contact with an infected rat or inhalation of air contaminated with rat excretions, like other hemorrhagic fevers, Lassa fever can be transmitted directly from one human to another. It can be contracted through direct contact with infected human blood excretions and secretions, including through sexual contact. No evidence of airborne transmission person-to-person is seen. Transmission through breast milk has also been observed.

Statistics: Lassa Fever

The number of Lassa virus infections per year in West Africa is estimated at 100,000 to 300,000, with approximately 5,000 deaths.

In 80% of cases, the disease is asymptomatic, but in the remaining 20%, it takes a complicated course. The virus is estimated to be responsible for about 5,000 deaths annually. The fever accounts for up to one third of deaths in hospitals within the affected regions and 10 to 16% of total cases.

The dissemination of the infection can be assessed by prevalence of antibodies to the virus in populations of: